It is known to use charging devices to charge a photosensitive member in electrophotographic printing. See, generally, R. M. Schaffert, The Focal Press, New York, 1965.
As is known, some charging devices include a control grid to regulate and control the charge provided to the photosensitive member, resulting in the photosensitive member receiving a uniform charge. Such charging devices with control grids are typically of the following types: scorotron, discorotron, and pin scorotron. Some benefits and problems associated with such control grids are discussed in Lewis E. Walkup, U.S. Pat. No. 2,777,957, especially FIGS. 4-7 and the text corresponding thereto. See also Geoffrey M. T. Foley, U.S. Pat. No. 4,638,397, especially columns 1-2.
To achieve uniform charging results, the control grid or screen must be parallel to the photosensitive member. A related requirement is that the control grid itself must be as flat as possible. This latter problem of control grid flatness is discussed in Joseph H. Lang et al., U.S. Pat. No. 4,792,680, especially columns 3-4.
The problem, therefore, is how to achieve a charging device with a flat control grid.
One existing method for achieving grid flatness is to form a grid from a stamped or etched hexagonal sheet stock, the grid being formed into a channel with side shields. While this method achieves a grid flatness of 0.25 to 0.50 mm, this method is not acceptable where a greater degree of flatness is required.
Another existing method for achieving grid flatness is to apply tension to the grid by means of springs and pulling tension at a singular point of grid attachment. This method, however, usually results in the unwanted curling or cupping of the grid. Moreover, this method is typically not useful where extrapolation to wide charge devices is required.
Therefore, there is a need for an improved charging device with a flat control grid.